EP0004509A2 - Refractory compositions for use in the production of injectable pastes having a low water content - Google Patents

Abstract

The invention relates to the field of refractory materials. It relates to refractory compositions comprising the following essential constituents: (1) 30 to 60% by weight of a coarse fraction consisting of grains of which more than 50% are greater than 0.5 mm; (2) 10 to 30% by weight of a fine fraction consisting of particles of which at least 50% are less than 75 microns; (3) 10 to 30% by weight of a very fine fraction made up of particles of which at least 50% are less than 5 microns; (4) 10 to 30% by weight of an ultra-fine fraction consisting of particles of which at least 80% are less than 0.1 microns; the fractions (1) to (4) being formed from mineral materials of natural or synthetic origin, inert with respect to water.

Description

The invention relates to refractory compositions useful for the production of injectable pastes with very low water content.

In the refractory products industry, pastes intended for injection into various steel, petrochemical or other devices are commonly manufactured each time a hot spot appears on an oven sheet metal. These hot spots can originate from the partial destruction of the refractory masonry or simply the opening of one or a few joints thus giving rise to a passage of hot gases.

This injection practice is common among others on blast furnaces, cowpers, hot wind pipes, primary or secondary petrochemical furnaces, transfer lines, etc.

Until now, the refractory pastes injected were mixtures of clays and chamotte sometimes enriched with a variable quantity of refractory cements. To obtain correctly injectable pasta, that is to say able to flow into cracks res or the packing agglomerates, it was almost always necessary to wet them with more than 15% water and, in most cases, more than 25%, or even more than 30% water. These contents give refractory masses, hardened and cooked, having porosities higher than 30% and sometimes reaching 40%.

• - la grande quantité d'eau nécessaire donne après séchage et éventuellement prise des produits poreux et peu résistants mécaniquement;
• - le départ brutal de ces importantes quantités d'eau projetée dans une maçonnerie chaude à tendance, par ailleurs, à créer dans les pâtes injectées de véritables canaux qui sont autant d'amorces de fissures pour de nouvelles fuites ou passages de gaz chauds.

These refractory pastes therefore have two major defects:

• - the large quantity of water required gives, after drying and possibly taken, porous products which are not mechanically resistant;
• - the sudden departure of these large quantities of water projected into hot masonry tending, moreover, to create in the injected pastes real channels which are as many incidences of cracks for new leaks or passages of hot gases.

To overcome this drawback, it was often necessary, after a first clogging by injection, to repeat a second or even a third injection in order to gradually block the nascent channels in the injected pasta.

The present invention aims to provide refractory compositions requiring, for obtaining injectable pastes, even under low pressures, only a reduced proportion of water, in any case less than 10% by weight, preferably between 4 and 8% by weight, these injectable pastes undergoing a total shrinkage due to drying and to the ceramic setting of less than 2%, preferably less than 1%.

• (1) 30 à 60%, et de préférence 40 à 50% en poids d'une fraction grossière constituée de grains dont au moins 50% sont supérieurs à 0,5 mm, les plus gros grains ne dépassant pas 10 mm, de préférence 6 mm;
• (2) 10 à 30%, de préférence 15 à 25%,en poids d'une fraction fine constituée de particules dont au moins 50% sont inférieures à 75 microns, les plus petites particules pouvant être de 10 microns;
• (3) 10 à 30%, de préférence 15 à 25%,en poids d'une fraction très fine constituée de particules dont au moins 50% sont inférieures à 5 microns, les plus fines particules pouvant être de 0,1 micron;
• (4) 10 à 30%, et de préférence 15 à 25%, en poids d'une fraction ultra-fine constituée de particules dont au moins 80% sont inférieures à 0,1 micron, les plus fines particules pouvant être de 0,01 micron;

les fractions (1) à (4) étant formées de matières minérales d'origine naturelle ou synthétique, inertes vis-à-vis de l'eau.The compositions of the invention comprise four essential constituents:

• (1) 30 to 60%, and preferably 40 to 50% by weight of a coarse fraction consisting of grains of which at least 50% are greater than 0.5 mm, the largest grains not exceeding 10 mm, preferably 6 mm;
• (2) 10 to 30%, preferably 15 to 25%, by weight of a fine fraction made up of particles of which at least 50% are less than 75 microns, the smallest particles possibly being 10 microns;
• (3) 10 to 30%, preferably 15 to 25%, by weight of a very fine fraction made up of particles of which at least 50% are less than 5 microns, the finest particles possibly being 0.1 micron;
• (4) 10 to 30%, and preferably 15 to 25%, by weight of an ultra-fine fraction made up of particles of which at least 80% are less than 0.1 micron, the finest particles possibly being 0, 01 micron;

the fractions (1) to (4) being formed of mineral materials of natural or synthetic origin, inert with respect to water.

The nature of the mineral materials forming fractions (1), (2) and (3) is not critical, it suffices that these materials are inert with respect to water. Fractions (1), (2) and (3) can be made of identical or different materials. By way of nonlimiting examples, the fractions (1), (2) and (3) may consist of materials chosen, independently, from the clay chamotte (that is to say from the cooked clay) , gibbsite, quartzite, alumina (corundum), magnesia, chromite, graphite, carbides, silicon nitrides and oxynitrides, "sialons" (ceramic materials made of solid solutions of Al ₂ O ₃ in silicon nitride Si ₃ N ₄ ), silicates, sand, refractory materials based on one or more metal oxides, powdered metals, etc.

The choice of the particular material or materials to use to constitute the fractions (1), (2) and (3) will depend on the temperature and the medium to which the injected paste will be subjected in service, as well as, of course, economic considerations. At present, clay chamotte is preferred when the temperatures encountered in service hardly exceed 1000 ^° C. approximately and alumina for higher temperatures (up to approximately 1500 ° C.).

Fractions (1), (2) and (3) can be easily obtained by mechanical grinding of the materials chosen and appropriate sieving,

The ultra-fine fraction (4), formed mainly of particles smaller than 0.1 micron can consist, for example, of silica, chromium oxide, titanium oxide, zirconium oxide, carbides of silicon, silicon nitrides and oxynitrides, etc ...

Alumina cannot be used to constitute fraction (4) because it is not possible to prepare ultra-fine particles of alumina which are inert with respect to water.

The ultra-fine fraction (4) cannot generally be obtained by mechanical grinding of the chosen material. The ultra-fine powders that can be used can be obtained in particular by known techniques for dissociation or hydrolysis of certain metallic compounds (such as halides) in the vapor phase, of condensation, from the vapor phase or from precipitation from solutions. in the case of oxides such as silica, chromium oxide, titanium oxide and zirconium oxide. Ultra-fine vitreous silica is also obtained as a by-product in certain industrial processes such as during reduction. tion of zirconium silicate in zirconia or during the production of ferro-silicon (the dust from electric ovens contains appropriate silica). Ultra-fine powders of silicon carbides, nitrides or oxynitrides can be obtained by spraying with a plasma torch.

Ultra-fine powders suitable as constituent (4) are commercially available or can be made suitable for use in the compositions of the invention by moderate calcination intended to make them inert with respect to water .

The components (1) to (4) must be inert with respect to water so as to form no colloid which, when swelling, would unnecessarily retain water.

To obtain injectable pastes, the compositions of the invention are mixed with an amount of water of less than 10% by weight, preferably between 4 and 8% by weight, until a homogeneous paste which flows by gravity. These pastes can be conveyed by all kinds of pumps for viscous fluids, such as piston pumps, pumps with offset axes, etc.

In order to facilitate wetting of the composition with water, it is advantageous to add a small amount (for example a few tenths of a percent) of organic or mineral dispersing agents, such as alkali metal phosphates, to the water. sodium tripolyphosphate.

The resulting pastes harden by ceramic setting (sintering) from 800 to 1000 ° C. The setting can be accelerated, if desired, by adding a few percent of alkali silicate, acid to the composition. phosphoric or hydraulic cements.

The property of the compositions of the invention of being able to form injectable pastes giving, after injection and cooking, products with low shrinkage (less than 2% and preferably less than 1%), seems to be due to the fact that one obtains very good filling of the cavities existing between the particles of a fraction given by the particles of the lower fraction so that the porosity of the cooked products is always less than 25% and preferably in the vicinity of 20%. Also, the ultra-fine particles seem to play the role of tiny "ball bearings" which make it possible to obtain pastes of excellent flowability despite the little water present and allow their injection under relatively low pressures.

The following nonlimiting examples illustrate the invention.

EXAMPLE 1 Clay Chamotte injectable paste:

• Composition by weight ... 48% clay chamotte to 42% Al ₂ O ₃ passing through a 2 mm sieve
• 20% chamotte clay to 42% ^of Al ₂ 0 ₃ of particle size 50% less than 75 microns
• 16% calcined Al ₂ O ₃ with a particle size less than 5 microns
• 12% condensed silica with a particle size less than 0.1 micron
• 4% "Sécar 250" cement (sold by Lafarge) 100%

Condensed silica less than 0.1 micron in size comes from the recovery in the suction sleeves of electric ferro-silicon furnaces.

Amount of water added for the preparation of an injectable paste at 20 bars ............ 7% by weight

• - à 150°C : densité apparente : 2,15
• - à 1000°C: densité apparente : 2,15 porosité ouverte : 22% Résistance à la compression : 400 kg/cm² Retrait : <0,2%

Physical properties after injection and cooking:

• - at 150 ° C: apparent density: 2.15
• - at 1000 ° C: apparent density: 2.15 open porosity: 22% Compressive strength: 400 kg / cm ² shrinkage: <0.2%

EXAMPLE 2 Injectable paste based on quartzite:

Quantité d'eau ajoutée pour la préparation d'une pâte injectable sous 20 bars ..... 6,5% en poids

Amount of water added for the preparation of a dough injectable at 20 bar ..... 6.5% by weight

• - à 150°C: densité apparente : 2,06
• - à 1000°C : densité apparente : 2,04 porosité ouverte : 20,8% résistance à la compression : 300 kg/cm² retrait : < 0,2%

Physical properties after injection and cooking:

• - at 150 ° C: apparent density: 2.06
• - at 1000 ° C: apparent density: 2.04 open porosity: 20.8% compressive strength: 300 kg / cm ² shrinkage: <0.2%

EXAMPLE 3

L'oxyde de chrome de grosseur inférieure à 0,1 micron est obtenu par précipitation à partir d'une solution et calcination à 700°C.Injectable paste based on alumina (corundum) and chromium oxide ^Cr ₂ ⁰ _3:

Chromium oxide smaller than 0.1 micron is obtained by precipitation from a solution and calcination at 700 ° C.

• - à 150°C : densité apparente : 2,85
• - à 1000°C : densité apparente : 2,89 Porosité ouverte : 20,1% Résistance à la compression : 600 kg/cm² Retrait : < 0,2%

Quantity of water added for the preparation of an injectable paste under 20 bars ..... 4.6% by weight Physical properties after injection and cooking:

• - at 150 ° C: apparent density: 2.85
• - at 1000 ° C: apparent density: 2.89 Open porosity: 20.1% Compressive strength: 600 kg / cm ² Shrinkage: <0.2%

EXAMPLE 4

Injection paste based on SiC:

Cubic SiC less than 0.08 micron in size is obtained by plasma torch spraying.

Quantity of water added for the preparation of an injectable paste at 20 bars ........... 4.8% by weight

• - à 150°C : densité apparente : 2,3
• - à 1000°C : densité apparente : 2,3 Porosité ouverte : 21% Résistance à la compression 250 kg/cm² Retrait : < 0,2%

Physical properties after injection and cooking:

• - at 150 ° C: apparent density: 2.3
• - at 1000 ° C: apparent density: 2.3 Open porosity: 21% Compressive strength 250 kg / cm ² Shrinkage: <0.2%

Claims (10)

1. Refractory compositions useful for the preparation of injectable pastes,
characterized in that they comprise the following essential constituents: (1) 30 to 60% by weight of a coarse fraction consisting of grains of which more than 50% are greater than 0.5 mm, the largest grains not exceeding 10 mm, preferably 6 mm; (2) 10 to 30% by weight of a fine fraction consisting of particles of which at least 50% are less than 75 microns, the smallest particles being able to be 10 microns; (3) 10 to 30% by weight of a very fine fraction made up of particles of which at least 50% are less than 5 microns, the finest particles being able to be 0.1 micron; (4) 10 to 30% by weight of an ultra-fine fraction made up of particles of which at least 80% are less than 0.1 micron, the finest particles possibly being 0.01 micron; the fractions (1) to (4) being formed from mineral materials of natural or synthetic origin, inert with respect to water. 2. Compositions according to claim 1, characterized in that the component (1) is present in an amount of 40 to 50% by weight and the components (2), (3) and (4) are each present in an amount of 15 to 25% by weight. 3. Compositions according to claim 1 or 2, characterized in that the fractions (1), (2) and (3) consist of identical or different materials chosen, independently, from clay chamotte, gibbsite, quartzite , alumina, magnesia, chromite, graphite, carbides, nitrides and and silicon oxynitrides, "Sialons", silicates, sand, refractory materials based on one or more metal oxides, and powdered metals. 4. Compositions according to claim 3, characterized in that at least one of the fractions (1), (2) and (3) is formed of clay or alumina chamotte. 5. Compositions according to any one of claims 1 to 4, characterized in that the ultra-fine fraction (4) consists of a material chosen from silica, chromium oxide, titanium dioxide, zirconium oxide, silicon carbides, silicon nitrides and silicon oxynitrides. 6. Compositions according to any one of claims 1 to 5, characterized in that they contain, in addition, a small amount of alkali silicate, phosphoric acid or hydraulic cement. 7. Injectable pastes characterized in that they consist of a composition according to any one of claims 1 to 6, mixed with a small amount of water less than 10% by weight. 8. Pasta according to claim 7, characterized in that the amount of mixed water is between 4 and 8% by weight. 9. Pasta according to claim 7 or 8, characterized in that the mixed water contains a small amount of a dispersing agent. 10. Pasta according to any one of claims 7 to 9, characterized in that they have a total shrinkage, after drying and ceramic setting, infe less than 2%, preferably less than 1%, and give cooked refractory masses with a porosity of less than 25%.